Coiled tubing systems are well known in the oil and gas industry. The term normally connotes a relatively small diameter continuous tubing string that can be transported to a well site on a drum or in a reel. Some methods for inserting coiled tubing systems into existing wells are well known in the art. As oil and gas exploration technology continues to improve the demand for better wellbore information grows and there has been more interest in using coiled tubing to deploy more instrumentation into the wellbore, particularly pressure and temperature sensors.
As fiber optic telemetry develops there is increased need to install multiple fiber optic sensors inside coiled tubing. Each sensor may require its own FIMT (Fiber In Metal Tubing), so there needs to be a method and devices to enable multiple FIMTs to be installed simultaneously in lengths of coiled tubing that can be up to 10 km.
A typical fiber telemetry system inside coiled tubing can consist of three fiber optic pressure transducers, one at the heel, one at the toe and one in the middle of the horizontal portion, along with additional fiber for DTS (Distributed Temperature Sensing) and/or DAS (Distributed Acoustic Sensing) telemetry. Each sensor may have single or multiple fibers, which are normally run inside FIMTs. Thus as many as 5 or more FIMTs may have to be installed in the coiled tubing at the same time. Although the number can vary the examples given in this disclosure will demonstrate the deployment of three fiber optic pressure transducers, one at the heel, one at the toe and one in the middle of the horizontal portion, along with additional fiber for DTS and/or DAS telemetry.
The installation of pressure transducers in three different locations along with the additional optical fibers for other sensors creates a need for a pressure housing for each pressure transducer that incorporates all of the needed sensing functionality while incorporating the capabilities for installation inside the cramped confines of coiled tubing. It is desirable to do this with approaches that result in little strain on the fibers, and in which there is no need for extensive cutting of the tubing in order to produce the coiled tube sensor assemblies.